Re: Stap is translating to functions in __exit sections...and later module load fails

[Eugeniy Meshcheryakov <eugeniy dot meshcheryakov at googlemail dot com>]

13 ÐÐÐÑÐÑ 2006 Ð 15:28 -0700 Stone, Joshua I ÐÐÐÐÑÐÐ(-ÐÐ):
> This seems to support the notion that the linker elided that function.
> 
> So, as Eugeniy wondered, why did the translator pick up that function at
> all?  I'm also curious what IP it chose for the kprobe, if the function
> no longer exists... Please try this command:
> 
> $ stap -p2 -vv -e 'probe kernel.function("exit_pfm_fs"){}' 2>&1 | grep
> 'pc='
> 
> I suspect that either elfutils is giving 'stale' debug information, or
> the translator is misinterpreting its results.
It loks like a bug in some version of gcc. I tried to compile the
following program with version from Debian stable and unstable on ia64:

$ cat test.c
static void __attribute__((section(".exit.text"))) exit_pfm_fs(void)
{
        return;
}
$

With gcc 3.3.5:

$ readelf -a test.o | grep exit_
     9: 0000000000000000    16 FUNC    LOCAL  DEFAULT    9 exit_pfm_fs
$ objdump -W test.o
...
The section .debug_info contains:

  Compilation Unit @ offset 0x0:
   Length:        52
   Version:       2
   Abbrev Offset: 0
   Pointer Size:  8
 <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
     DW_AT_stmt_list   : 0
     DW_AT_name        : (indirect string, offset: 0x38): test.c
     DW_AT_comp_dir    : (indirect string, offset: 0x0): /home/eugen
     DW_AT_producer    : (indirect string, offset: 0xc): GNU C 3.3.5
(Debian 1:3.3.5-13)
     DW_AT_language    : 1      (ANSI C)
 <1><1d>: Abbrev Number: 2 (DW_TAG_subprogram)
     DW_AT_name        : (indirect string, offset: 0x2c): exit_pfm_fs
     DW_AT_decl_file   : 1
     DW_AT_decl_line   : 2
     DW_AT_prototyped  : 1
     DW_AT_low_pc      : 0
     DW_AT_high_pc     : 0x10
     DW_AT_frame_base  : 1 byte block: 5c       (DW_OP_reg12)
...
$

With gcc 4.1.2:

$ readelf -a t.o | grep exit_
$ objdump -W t.o | grep exit_
objdump: Error: No comp units in .debug_info section ?objdump: Error: No
comp units in .debug_info section ?$


-- 
Eugeniy Meshcheryakov

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